This invention relates to aqueous coating solutions comprising gelatin which is prepared by the hydrolysis of ossein using sodium or potassium hydroxide, where the coating solution contains a colloidal particle dispersed material phase at a volume fraction of at least 0.01.
Imaging elements, particularly photographic silver halide imaging elements, commonly use a hydrophilic colloid as a film forming binder for layers thereof, most commonly ossein. The layers of such imaging elements are typically coated employing multilayer slide bead coating processes such as described in U.S. Pat. No. 2,716,419 and multilayer slide curtain coating processes such as described in U.S. Pat. No. 3,508,947. The binder of choice in most cases is gelatin, prepared from various sources of collagen (see, e.g., P. I. Rose, The Theory of Photographic Process, 4th Edition, edited by T. H. James (Macmillan Publishing Company, New York, 1977) p. 51-65). The binder is expected to provide several functions, primarily to provide an element with some level of mechanical integrity and contain all the materials within the imaging element, which are required to provide an image.
The various layers of imaging elements comprising gelatin are typically coated from aqueous coating solutions. In addition to serving as a binder, gelatin also functions as a stabilizer to dispersed aqueous insoluble materials of colloidal dimensions which may also be present in the aqueous coating solutions. Such materials can include photographically-useful materials such as coupler drops, UV-absorbers, scavengers of oxidized developer, silver halide grains, dye particles or materials needed for other functions, such as polymer latexes and silica particles. A colloidal dispersed material particle has at least one dimension in the range 1 nm to 1 xcexcm. The viscosity of fluids containing gelatin and such colloidal materials is an important parameter affecting the efficiency of the manufacture of imaging materials such as photographic products. The most important impact of viscosity is on the coating process. If the viscosity is too high, then the fluid cannot be pumped sufficiently fast. If the viscosity is too low then defects may arise due to ripple, flow on the web after coating and failure of the multilayer pack to gel thermally (chill set). Coating fluid viscosity increases with gelatin and dispersed phase concentrations, as the mean molecular weight of the gelatin increases, and as the size of dispersed colloidal particles decreases. One of the most expensive processes in manufacturing of multilayer photographic products is drying of water after coating. If the concentration of solids within the coating fluid can be increased, then less water is coated and less drying is required at a given coating speed (or the coating speed can be increased without increasing the throughput capacity of the dryers). However, as the concentration increases, the viscosity of the coating fluid may become too high to pump easily and the coating fluids may exhibit too much shear thinning (viscosity decreasing as shear rate increases) to give uniform laydown across the web.
It is well recognised that the presence of sub-micron colloidal particles increases the viscosity of gelatin solutions. For a given volume fraction of colloidal material, the viscosity increases as the particle size of the colloid is reduced. The affect arises through adsorption of gelatin to the surfaces of the dispersed particles leading to an increase in the effective volume occupied by the colloid. Examples are given, e.g., in the following references: Howe A M, Clarke A and Whitesides T H, xe2x80x9cViscosity of Emulsions of Polydisperse Droplets with a Thick Adsorbed Layerxe2x80x9d Langmuir 13:2617-2626 (1997); Dreja M, Heine K, Tieke B and Junkers G, xe2x80x9cEffects of functionalized latex particles and anionic surfactants on the flow behavior of aqueous gelatin dispersionsxe2x80x9d J. Colloid Interface Sci. 191(1):131-140 (1997); Vaynberg K A, Wagner N J, Sharma R and Martic P, xe2x80x9cStructure and extent of adsorbed gelatin on acrylic latex and polystyrene colloidal particlesxe2x80x9d J. Colloid Interface Sci., 205:131-140 (1998); Hone J H E, Howe A M and Whitesides T H, xe2x80x9cRheology of polystyrene latexes with adsorbed and free gelatinxe2x80x9d Colloids Surfaces 161:283-306 (2000); Vaynberg K A and Wagner N J, xe2x80x9cRheology of polyampholyte (gelatin)-stabilised colloidal dispersions: The tertiary electroviscous effectxe2x80x9d J. Rheology 45(2):451-466 (2001).
For various applications, it would be desirable to be able to increase the concentration of a coating fluid containing gelatin and dispersed sub-micron colloidal materials, reduce the size of the sub-micron colloidal materials in such a coating fluid, and/or enable the inclusion of higher molecular weight gelatin in such a coating fluid without detrimentally increasing the viscosity. For other applications, it would be desirable to be able to reduce the viscosity of an aqueous coating fluid containing gelatin and dispersed insoluble colloidal material without needing to reduce the concentration of gelatin or colloidal materials, increase the size of the sub-micron colloidal materials, and/or reduce the molecular weight of the gelatin. It would further be desirable to be able to make such changes, either singly or in combinations thereof, without fundamentally changing the composition of the materials in the coating fluid, or otherwise having to use undesirable conditions with respect to temperature (viscosity typically decreases with increasing T), pH (viscosity typically decreases with reducing pH) or ionic strength (adding salts typically causes viscosity to decrease).
High purity gelatins are generally required for imaging applications. Currently the most commonly employed manufacturing process for obtaining high purity gelatins involves demineralization of a collagen containing material, typically cattle bone (ossein), followed by extended alkaline treatment (liming) and finally gelatin extractions with water of increasing temperature as described in U.S. Pat. Nos. 3,514,518 and 4,824,939. The gelatin produced by this process, commonly referred to as lime processed ossein gelatin, has existed with various modifications throughout the gelatin industry for a number of years. The liming step of this process requires up to 60 days or more, the longest step in the approximately 3 month process of producing gelatin. The hydrolyzed collagen is extracted in a series of steps to obtain several gelatin fractions with varying molecular weights. In order to obtain gelatin of desired molecular weight to provide suitable coating solution viscosities, these fractions can be further hydrolyzed by high temperature hydrolysis. The fractions are then blended to obtain the appropriate molecular weight for photographic use. U.S. Pat. No. 5,908,921 describes a relatively new process for the preparation of photographic grade gelatin, where the agent for hydrolysis is a strong alkali, such as sodium or potassium hydroxide. The reaction rate is disclosed to be from 10 to 120 hours (substantially faster than the prior lime processes), after which a single extraction step yields a single batch of gelatin, which is then purified and deionized. The characteristics of the gelatin produced are that it has a high gel strength and narrow molecular weight distribution compared to gelatins produced by the conventional process where lime is used as the agent for hydrolysis. There is no disclosure in U.S. Pat. No. 5,908,921, however, regarding any possible impact use of the gelatin produced by such process may have on aqueous coating fluids containing such gelatin and dispersed colloidal material.
In accordance with the invention, an aqueous coating fluid is described comprising gelatin at a concentration of at least 1 wt % and a colloidal particle dispersed material phase at a volume fraction of at least 0.01, wherein at least 20% of the gelatin comprises a gelatin prepared from hydrolysis of ossein using sodium or potassium hydroxide.
The present invention enables increasing the concentrations of a coating fluid containing gelatin and dispersed sub-micron colloidal materials, reducing the size of the sub-micron colloidal materials in such a coating fluid, and/or including higher molecular weight gelatin in such a coating fluid without detrimentally increasing the viscosity of such fluids. The invention further enables reducing the viscosity of an aqueous coating fluid containing gelatin and dispersed insoluble colloidal material, without needing to reduce the concentration of gelatin or colloidal materials, increase the size of the sub-micron colloidal materials, and/or reduce the molecular weight of the gelatin. Each such advantage may be achieved either individually, or in combinations to varying extents, without the need to fundamentally change the composition of the materials in the coating fluid.
Aqueous coating fluids in accordance with the invention comprise at least 1 wt % gelatin, and at least 0.01 volume fraction of a colloidal particle dispersed material phase. The dispersed material may be a dispersion of any colloidal organic or inorganic material useful in imaging elements, and in particular photographically useful materials, such as dispersed photographic coupler drops, UV-absorbers, scavengers of oxidized developer, silver halide grains, dye particles or other materials needed for other functions in an imaging element, such as polymer latexes and silica particles. The invention is particularly useful with respect to coating fluids comprising a colloidal dispersed material phase wherein the number mean particle diameter of dispersed colloidal material comprising at least 0.01 volume fraction is less than 1 micrometer, and more particularly less than 0.3 micrometer, and more preferably where dispersed colloidal material of such mean particle sizes comprise a volume fraction of the coating fluid of at least 0.03, as such coating fluids are generally more liable to otherwise result in higher than desired coating viscosities as a result of interactions between the gelatin and the dispersed material phase. Preparation of colloidal dispersions of hydrophic materials for use in the coating fluids of the invention is itself not critical, and any known dispersion forming techniques (e.g., high pressure emulsification, mill grinding, precipitation, etc.) may be used.
High purity gelatins are required for imaging/photographic applications. One gelatin property of interest is absorbance at 420 nm (A420), commonly know as color. The lower the A420 of gelatin the clearer the gelatin layer is in coated products. The A420 of gelatin is one of the defining factors for determining applicability of the gelatin for imaging applications. Edible gelatins are typically higher than photographic gelatins in A420. Two other gelatin properties critical to imaging applications are viscosity and gel strength or Bloom. Ideally, use of a gelatin with relatively high gel strength and low viscosity would be advantageous to coated products, in that high gel strength is desired for gelatin setting properties, while coating speeds could be increased with lower viscosity gelatins (through lower viscosity at same concentration increasing the onset of air entrainment or lower wet laydown at same low-shear viscosity reducing the energy required to remove the water). Due to variable bond breakage during manufacture, gelatin is composed of a distribution of polypeptides of varying molecular weights. Aqueous size exclusion chromotagraphy provides a method of analysis for determining the gelatin molecular weight distribution. This distribution is described as containing the following fractions; high molecular weight or HMW ( greater than 250 kD); Beta (250-150 kD); Alpha (150-50 kD); Subalpha (50-20 kD); and low molecular weight or LMW (20-4 kD). In general, high gel strength correlates with high gelatin alpha fraction content, and high viscosity correlates with high gelatin HMW fraction content. The viscosity of a gelatin solution at a specified concentration is itself often used to characterize the mean molecular weight of a particular gelatin sample. Typical alkaline processed bone gelatins contain relatively high gel strength and high viscosity. Gelatin viscosity can be controlled during the gelatin manufacturing process with heat treatment. Heat treatment, however, reduces both gel strength and viscosity. Typical gel strengths are from 250 to 300 Bloom and typical viscosities are from 5 to 15 mPa.s (for a 6.16 wt % gelatin solution, measured at 40 C.).
At least 20% of the gelatin of an aqueous coating fluid comprising gelatin and a colloidal dispersed material phase in accordance with the invention comprises a gelatin prepared from a process comprising hydrolysis of ossein utilizing a caustic sodium or potassium hydroxide solution to produce gelatin from a collagen containing material, such as described in U.S. Pat. No. 5,908,921, the disclosure of which is incorporated by reference herein. The process for the manufacture of gelatin as taught in U.S. Pat. No. 5,908,921 includes providing a collagen containing material and demineralizing the collagen containing material to produce ossein which is homogenized or ground. The ossein is added to a water solution of sodium hydroxide or potassium hydroxide at a concentration of at least 4% by weight and a swelling restraining salt (ie. sodium sulfate) at a concentration of at least 3% by weight for a time sufficient (typically 10 to 120 hours) to form a reacted slurry. The slurry is heated at a temperature of at least 45 C. for a time sufficient (typically at least 30 minutes) to produce a gelatin containing solution. The gelatin containing solution is clarified by raising the pH of the solution to greater than 9.8. A sulfate salt of a divalent or trivalent metal is added to the gelatin solution to reduce the pH to between 7.0 and 8.0. An acid, preferably phosphoric, is added to the solution to reduce the pH to between 5.0 and 6.0. A polymeric flocculant is added to the gelatin containing solution at a weight percent of 0.1 based on the dry weight of the gelatin to form a floc which is removed. Following extraction and clarification the gelatin solution is filtered, oxidized or deionized to achieve desired levels of microconstituents, prior to concentration and drying. The rate of reaction with the collagen is a function of caustic concentration, salt concentration, temperature and time. The process is further specifically illustrated by Example 1 of U.S. Pat. No. 5,908,921.
Typical collagen containing materials include skins, bones and hides (i.e., any connective tissue of an animal body). Sources of animal bodies include cattle, pigs and sheep. Cattle bone is preferred, although other sources of bone can be effectively utilized in the present invention. A continuous process for leaching cattle bone is described in U.S. Pat. No. 4,824,939, incorporated herein by reference. In this process the bovine bone is placed into contact with an acid, typically hydrochloric acid. The acid reacts with the minerals contained in the bone to form soluble products, such as calcium chloride and phosphoric acid. These products are leached out of the bone and removed, typically as calcium hydrogen phosphate dihydrate. The demineralized bone or ossein is one source of collagen from which gelatin can be extracted.
A gelatin prepared by hydrolysis of ossein using sodium or potassium hydroxide as described above and which is employed in the coating fluids of the invention is hereafter referred to as a xe2x80x9csolubilized collagenxe2x80x9d gelatin, as collagen from the source material is completely solubilized. Gelatin obtained therefrom is dissolved in a single extraction, and the described process advantageously creates a very uniform gelatin with minimal time and energy. The extracted gelatin may be purified through the use of a clarification process and desalted, typically using ultrafiltration or electrodialysis technology. Although the molecular weight of the gelatin obtained may be relatively high (such as obtained in U.S. Pat. No. 5,908,921 Example 1), the proteolytic degradation of gelatin (such as disclosed, e.g., in U.S. Pat. Nos. 5,919,906, 6,080,843, and 6,100,381) can be advantageously used to reduce the molecular weight to a desired range. The characteristics of the gelatin produced, using these methods is that it has a relatively high gel strength and narrow molecular weight distribution compared to gelatins produced by the conventional process where lime is used as the agent for hydrolysis. It has been surprisingly found that use of solubilized collagen gelatin with such relatively narrow molecular weight distribution in aqueous coating fluids with a colloidal dispersed material phase in accordance with the invention enables relative improvements in obtaining a desired coating fluid viscosity.
In a particular embodiment of the invention, coating fluids comprising a colloidal particle dispersed material phase and a solubilized collagen gelatin which has a solution viscosity of greater than 3 mPa.s, more preferably greater than 4 mPa.s, where the solution viscosity is that of a 6.16 wt % gelatin solution, measured at 40 C., may advantageously be formulated without generating an undesirable coating fluid visosity observed with use of solely conventional lime-processed gelatins of similar solution viscosities in such coating fluids.
While aqueous coatings fluids in accordance with the invention comprise at least 1 wt % gelatin, the advantages provided by the invention are particularly applicable to higher concentration coating fluids, such as coating fluids comprising 3 wt % gelatin or more, preferably 4 wt % gelatin or more, and especially 5 wt % gelatin or more, which contain a colloidal particle dispersed material phase at a volume fraction of at least 0.01, preferably at least 0.03. Replacement of the gelatin in a coating fluid with a solubilized collagen gelatin in accordance with the invention provides a manufacturing improvement proportional to the fraction of solubilized collagen gelatin present. Thus, while the present invention is broadly directed towards the use of solubilized collagen gelatin in an amount of at least 20% of the gelatin in the coating fluid, it is preferable to have at least 30%, more preferably at least 40%, and most preferable at least 50% of solubilized collagen gelatin as the gelatin in the coating fluids of the invention. In a specific embodiment of the invention, the coating fluid may further comprise an anionic polymeric thickener where desired, e.g., at a concentration above 0.01% wt %. The advantages of the invention are applicable to coating fluids prepared for multilayer slide bead coating processes such as described in U.S. Pat. No. 2,716,419 as well as multilayer slide curtain coating processes such as described in U.S. Pat. No. 3,508,947.
Gelatin layers of imaging elements are frequently desirably cross-linked or hardened by reaction with a gelatin hardener in order to improve the physical properties of the layer. In addition to providing coating fluid viscosity advantages, the use of solubilized collagen gelatin in combination with certain effective amounts of gelatin hardener in imaging elements has been found to enable relative improvements in the wet mechanical strength of an imaging element comprising gelatin as a binder, without needing to increase the amount of chemical crosslinker with respect to the gelatin. Imaging elements comprising a specified level of solubilized collagen gelatin in one or more hydrophilic colloid layer thereof in combination with a specified effective level of gelatin hardener per gram of gelatin are described in commonly assigned, concurrently-filed, co-pending application U.S. Ser. No. 10/158,656 (Kodak Docket 83063AJA), the disclosure of which is incorporated herein by reference. The hardener in such imaging elements may be delivered through the coating fluid comprising the solubilized collagen gelatin, or a separate hardener-bearing layer coated therewith.
Coating fluids comprising gelatin and a colloidal particle dispersed hydrophic material phase in accordance with the invention may additionally comprise effective levels of any conventional hardener. A further advantage to the use of solubilized collagen gelatin in aqueous coating fluids is that for coating fluids comprising gelatin and gelatin hardener which have similar concentrations and viscosities, the time for formation of gel slugs to be formed in a hardener-bearing coating fluid may be significantly extended when a solubilized collagen gelatin is employed rather than a conventional lime processed gelatin. Coating fluids containing specified levels of solubilized collagen gelatin and gelatin hardener are described in commonly assigned, concurrently-filed, co-pending application U.S. Ser. No. 10/158,681 (Kodak Docket 83293AJA), the disclosure of which is incorporated herein by reference.
Coating fluids of the invention may be employed in the manufacture of many different types of imaging elements, depending on the particular use for which they are intended. Details with respect to the composition and function of a wide variety of different imaging elements are provided in U.S. Pat. No. 5,300,676 and references described therein. Such elements include, for example, photographic, electrophotographic, electrostatographic, photothermographic, migration, electrothermographic, dielectric recording and thermal-dye-transfer imaging elements. Layers of imaging elements other than the image-forming layer are commonly referred to auxiliary layers. There are many different types of auxiliary layers such as, for example, subbing layers, backing layers, interlayers, overcoat layers, receiving layers, stripping layers, antistatic layers, transparent magnetic layers, and the like.
The coating fluids of this invention in particular may be used in the manufacture of photographic elements, such as photographic films, photographic papers or photographic glass plates, in which the image-forming layer is a radiation-sensitive silver halide emulsion layer. The thickness of the support is not critical. Film support thickness of 2 to 10 mil (0.06 to 0.30 millimeters), and thicker paper supports, e.g., typically can be used. The supports typically employ an undercoat or subbing layer well known in the art that comprises, for example, for polyester support a vinylidene chloride/methyl acrylate/itaconic acid terpolymer or vinylidene chloride/acrylonitrile/acrylic acid terpolymer. The emulsion layers typically comprise a film-forming hydrophilic colloid. The most commonly used of these is gelatin and a solubilized collagen gelatin as described above is a particularly preferred material for use in photographic emulsion layers in such embodiments.
Photographic imaging elements can be black and white, single color or multicolor photographic elements. Multicolor elements contain dye image-forming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as known in the art. In an alternative format, the emulsions sensitive to each of the three primary regions of the spectrum can be disposed as a single segmented layer. Depending upon the dye-image-providing material employed in the photographic element, it can be incorporated in the silver halide emulsion layer or in a separate layer associated with the emulsion layer. The dye-image-providing material can be any of a number known in the art, such as dye-forming couplers, bleachable dyes, dye developers and redox dye-releasers, and the particular one employed will depend on the nature of the element, and the type of image desired. Dye-image-providing materials employed with conventional color photographic materials designed for processing with a separate developing solution are preferably dye-forming couplers; i.e., compounds which couple with oxidized developing agent to form a dye. Preferred couplers which form cyan dye images are phenols and naphthols. Preferred couplers which form magenta dye images are pyrazolones and pyrazolotriazoles. Preferred couplers which form yellow dye images are benzoylacetanilides and pivalylacetanilides.
A typical multicolor photographic element comprises a support bearing a cyan dye image-forming unit comprised of at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, and a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler. The element can contain additional layers, such as filter layers, interlayers, overcoat layers, subbing layers, and the like. All of these can be coated on a support which can be transparent or reflective (for example, a paper support). Photographic elements may also usefully include a magnetic recording material as described in Research Disclosure, Item 34390, November 1992, or a transparent magnetic recording layer such as a layer containing magnetic particles on the underside of a transparent support as in U.S. Pat. Nos. 4,279,945 and 4,302,523. The element typically will have a total thickness (excluding the support) of from 5 to 30 microns. While the order of the color sensitive layers can be varied, they will normally be red-sensitive, green-sensitive and blue-sensitive, in that order on a transparent support, (that is, blue sensitive furthest from the support) and the reverse order on a reflective support being typical. The present invention also contemplates the use of photographic imaging elements in accordance with of the present invention in what are often referred to as single use cameras (or xe2x80x9cfilm with lensxe2x80x9d units). These cameras are sold with film preloaded in them and the entire camera is returned to a processor with the exposed film remaining inside the camera. Such cameras may have glass or plastic lenses through which the photographic element is exposed.
In the following discussion of suitable materials for use in imaging elements, reference will be made to Research Disclosure, September 1994, Number 365, Item 36544, which will be identified hereafter by the term xe2x80x9cResearch Disclosure I.xe2x80x9d The Sections hereafter referred to are Sections of the Research Disclosure I unless otherwise indicated. All Research Disclosures referenced are published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire P010 7DQ, ENGLAND. The foregoing references and all other references cited in this application, are incorporated herein by reference.
Silver halide emulsions which may be employed in photographic imaging elements may be negative working, such as surface sensitive emulsions or unfogged internal latent image forming emulsions, or positive working emulsions of internal latent image forming emulsions (that are either fogged in the element or fogged during processing). With negative working silver halide a negative image can be formed; optionally, a positive (or reversal) image can be formed although a negative image is typically first formed in the reversal process. Suitable emulsions and their preparation as well as methods of chemical and spectral sensitization are described in Sections I through V. Color materials and development modifiers are described in Sections V through XX. Vehicles (which can be used in combination with solubilized collagen gelatin in photographic imaging elements in accordance with the invention) are described in Section II, and various additives such as brighteners, antifoggants, stabilizers, light absorbing and scattering materials, hardeners, coating aids, plasticizers, lubricants and matting agents are described, for example, in Sections VI through XIII. Manufacturing methods are described in all of the sections, layer arrangements particularly in Section XI, exposure alternatives in Section XVI, and processing methods and agents in Sections XIX and XX.
Photographic imaging elements may also use colored couplers (e.g. to adjust levels of interlayer correction) and masking couplers such as those described in EP 213 490; Japanese Published Application 58-172,647; U.S. Pat. No. 2,983,608; German Application DE 2,706,117C; U.K. Patent 1,530,272; Japanese Application A-113935; U.S. Pat. No. 4,070,191 and German Application DE 2,643,965. The masking couplers may be shifted or blocked.
Photographic imaging elements may also contain materials that accelerate or otherwise modify the processing steps of bleaching or fixing to improve the quality of the image. Bleach accelerators described in EP 193 389; EP 301 477; U.S. Pat. Nos. 4,163,669; 4,865,956; and 4,923,784 are particularly useful. Also contemplated is the use of nucleating agents, development accelerators or their precursors (UK Patent 2,097,140; U.K. Patent 2,131,188); electron transfer agents (U.S. Pat. Nos. 4,859,578; 4,912,025); antifogging and anti color-mixing agents such as derivatives of hydroquinones, aminophenols, amines, gallic acid; catechol; ascorbic acid; hydrazides; sulfonamidophenols; and non color-forming couplers.
Imaging elements may also contain other filter dye layers comprising colloidal silver sol or yellow and/or magenta filter dyes and/or antihalation dyes (particularly in an undercoat beneath all light sensitive layers or in the side of the support opposite that on which all light sensitive layers are located) either as oil in water dispersions, latex dispersions or as solid particle dispersions. Additionally, they may be used with xe2x80x9csmearingxe2x80x9d couplers (e.g. as described in U.S. Pat. No. 4,366,237; EP 096 570; U.S. Pat. Nos. 4,420,556; and 4,543,323.) Also, the couplers may be blocked or coated in protected form as described, for example, in Japanese Application 61/258,249 or U.S. Pat. No. 5,019,492.
Photographic imaging elements may further contain other image-modifying compounds such as xe2x80x9cDeveloper Inhibitor-Releasingxe2x80x9d compounds (DIR""s). Useful additional DIR""s for elements of the present invention, are known in the art and examples are described in U.S. Pat. Nos. 3,137,578; 3,148,022; 3,148,062; 3,227,554; 3,384,657; 3,379,529; 3,615,506; 3,617,291; 3,620,746; 3,701,783; 3,733,201; 4,049,455; 4,095,984; 4,126,459; 4,149,886; 4,150,228; 4,211,562; 4,248,962; 4,259,437; 4,362,878; 4,409,323; 4,477,563; 4,782,012; 4,962,018; 4,500,634; 4,579,816; 4,607,004; 4,618,571; 4,678,739; 4,746,600; 4,746,601; 4,791,049; 4,857,447; 4,865,959; 4,880,342; 4,886,736; 4,937,179; 4,946,767; 4,948,716; 4,952,485; 4,956,269; 4,959,299; 4,966,835; 4,985,336 as well as in patent publications GB 1,560,240; GB 2,007,662; GB 2,032,914; GB 2,099,167; DE 2,842,063, DE 2,937,127; DE 3,636,824; DE 3,644,416 as well as the following European Patent Publications: 272,573; 335,319; 336,411; 346,899; 362,870; 365,252; 365,346; 373,382; 376,212; 377,463; 378,236; 384,670; 396,486; 401,612; 401,613. DIR compounds are also disclosed in xe2x80x9cDeveloper-Inhibitor-Releasing (DIR) Couplers for Color Photography,xe2x80x9d C. R. Barr, J. R. Thirtle and P. W. Vittum in Photographic Science and Engineering, Vol. 13, p. 174 (1969), incorporated herein by reference.
It is also contemplated that the present invention may be employed to obtain reflection color prints as described in Research Disclosure, November 1979, Item 18716, available from Kenneth Mason Publications, Ltd, Dudley Annex, 12a North Street, Emsworth, Hampshire P0101 7DQ, England, incorporated herein by reference. The emulsions and materials to form imaging elements may be coated on pH adjusted support as described in U.S. Pat. No. 4,917,994; with epoxy solvents (EP 0 164 961); with additional stabilizers (as described, for example, in U.S. Pat. Nos. 4,346,165; 4,540,653 and 4,906,559); with ballasted chelating agents such as those in U.S. Pat. No. 4,994,359 to reduce sensitivity to polyvalent cations such as calcium; and with stain reducing compounds such as described in U.S. Pat. Nos. 5,068,171 and 5,096,805. Other compounds useful in imaging elements are disclosed in Japanese Published Applications 83-09,959; 83-62,586; 90-072,629, 90-072,630; 90-072,632; 90-072,633; 90-072,634; 90-077,822; 90-078,229; 90-078,230; 90-079,336; 90-079,338; 90-079,690; 90-079,691; 90-080,487; 90-080,489; 90-080,490; 90-080,491; 90-080,492; 90-080,494; 90-085,928; 90-086,669; 90-086,670; 90-087,361; 90-087,362; 90-087,363; 90-087,364; 90-088,096; 90-088,097; 90-093,662; 90-093,663; 90-093,664; 90-093,665; 90-093,666; 90-093,668; 90-094,055; 90-094,056; 90-101,937; 90-103,409; 90-151,577.
Silver halide used in photographic imaging elements may be silver iodobromide, silver bromide, silver chloride, silver chlorobromide, silver chloroiodobromide, and the like. For example, in one particular embodiment, the silver halide used in photographic imaging elements of the present invention may contain at least 90 mole % silver chloride or more (for example, at least 95%, 98%, 99% or 100% silver chloride). The type of silver halide grains preferably include polymorphic, cubic, and octahedral. The grain size of the silver halide may have any distribution known to be useful in photographic compositions, and may be either polydipersed or monodispersed.
Tabular grain silver halide emulsions may also be used. Tabular grains are those with two parallel major faces each clearly larger than any remaining grain face (e.g., ECD/t is at least 2, where ECD is the diameter of a circle having an area equal to grain projected area and t is tabular grain thickness), and tabular grain emulsions are those in which the tabular grains account for at least 50 percent, preferably at least 70 percent and optimally at least 90 percent of total grain projected area. The tabular grains can account for substantially all (e.g., greater than 97 percent) of total grain projected area. The tabular grain emulsions can be high aspect ratio tabular grain emulsionsxe2x80x94i.e., ECD/t greater than 8; intermediate aspect ratio tabular grain emulsionsxe2x80x94i.e., ECD/t=5 to 8; or low aspect ratio tabular grain emulsionsxe2x80x94i.e., ECD/t=2 to 5. The emulsions preferably typically exhibit high tabularity (T), where T (i.e., ECD/t2) greater than 25 and ECD and t are both measured in micrometers (xcexcm). The tabular grains can be of any thickness compatible with achieving an aim average aspect ratio and/or average tabularity of the tabular grain emulsion. Preferably the tabular grains satisfying projected area requirements are those having thicknesses of  less than 0.3 xcexcm, thin ( less than 0.2 xcexcm) tabular grains being specifically preferred and ultrathin ( less than 0.07 xcexcm) tabular grains being contemplated for maximum tabular grain performance enhancements. When the native blue absorption of iodohalide tabular grains is relied upon for blue speed, thicker tabular grains, typically up to 0.5 xcexcm in thickness, are contemplated. Tabular grains formed of silver halide(s) that form a face centered cubic (rock salt type) crystal lattice structure can have either {100} or {111} major faces.
Silver halide grains may be prepared according to methods known in the art, such as those described in Research Disclosure I and James, The Theory of the Photographic Process. These include methods such as ammoniacal emulsion making, neutral or acidic emulsion making, and others known in the art. These methods generally involve mixing a water soluble silver salt with a water soluble halide salt in the presence of a protective colloid, and controlling the temperature, pAg, pH values, etc, at suitable values during formation of the silver halide by precipitation.
Silver halide grains may be advantageously subjected to chemical sensitization with noble metal (for example, gold) sensitizers, middle chalcogen (for example, sulfur) sensitizers, reduction sensitizers and others known in the art. Compounds and techniques useful for chemical sensitization of silver halide are known in the art and described in Research Disclosure I and the references cited therein.
Photographic imaging elements provide the silver halide in the form of an emulsion. Photographic emulsions generally include a vehicle for coating the emulsion as a layer of a photographic element. Useful vehicles include both naturally occurring substances such as proteins, protein derivatives, cellulose derivatives (e.g., cellulose esters), gelatin (e.g., alkali-treated gelatin such as cattle bone or hide gelatin, or acid treated gelatin such as pigskin gelatin), gelatin derivatives (e.g., acetylated gelatin, phthalated gelatin, and the like), and others as described in Research Disclosure I. Also useful as vehicles or vehicle extenders are hydrophilic water-permeable colloids. These include synthetic polymeric peptizers, carriers, and/or binders such as poly(vinyl alcohol), poly(vinyl lactams), acrylamide polymers, polyvinyl acetals, polymers of alkyl and sulfoalkyl acrylates and methacrylates, hydrolyzed polyvinyl acetates, polyamides, polyvinyl pyridine, methacrylamide copolymers, and the like, as described in Research Disclosure I. The vehicle can be present in the emulsion in any amount useful in photographic emulsions. The emulsion can also include any of the addenda known to be useful in photographic emulsions. These include chemical sensitizers, such as active gelatin, sulfur, selenium, tellurium, gold, platinum, palladium, iridium, osmium, rhenium, phosphorous, or combinations thereof. Chemical sensitization is generally carried out at pAg levels of from 5 to 10, pH levels of from 5 to 8, and temperatures of from 30 to 80 C., as described in Research Disclosure I, Section IV (pages 510-511) and the references cited therein.
The silver halide may be sensitized by sensitizing dyes by any method known in the art, such as described in Research Disclosure I. The dye may be added to an emulsion of the silver halide grains and a hydrophilic colloid at any time prior to (e.g., during or after chemical sensitization) or simultaneous with the coating of the emulsion on a photographic element. The dyes may, for example, be added as a solution in water or an alcohol. The dye/silver halide emulsion may be mixed with a dispersion of color image-forming coupler immediately before coating or in advance of coating (for example, 2 hours).
Photographic imaging elements are preferably imagewise exposed using any of the known techniques, including those described in Research Disclosure I, section XVI. This typically involves exposure to light in the visible region of the spectrum, and typically such exposure is of a live image through a lens, although exposure can also be exposure to a stored image (such as a computer stored image) by means of light emitting devices (such as light emitting diodes, CRT and the like).
Photographic imaging elements can be processed in any of a number of well-known photographic processes utilizing any of a number of well-known processing compositions, described, for example, in Research Disclosure I, or in T. H. James, editor, The Theory of the Photographic Process, 4th Edition, Macmillan, N.Y., 1977. In the case of processing a negative working element, the element is treated with a color developer (that is one which will form the colored image dyes with the color couplers), and then with a oxidizer and a solvent to remove silver and silver halide. In the case of processing a reversal color element, the element is first treated with a black and white developer (that is, a developer which does not form colored dyes with the coupler compounds) followed by a treatment to fog silver halide (usually chemical fogging or light fogging), followed by treatment with a color developer. Preferred color developing agents are p-phenylenediamines. Especially preferred are: 4-amino N,N-diethylaniline hydrochloride, 4-amino-3-methyl-N,N-diethylaniline hydrochloride, 4-amino-3-methyl-N-ethyl-N-(b-(methanesulfonamido)ethylaniline sesquisulfate hydrate, 4-amino-3-methyl-N-ethyl-N-(b-hydroxyethyl)aniline sulfate, 4-amino-3-b-(methanesulfonamido)ethyl-N,N-diethylaniline hydrochloride and 4-amino-N-ethyl-N-(2-methoxyethyl)-m-toluidine di-p-toluene sulfonic acid. Development is followed by bleach-fixing, to remove silver or silver halide, washing and drying.